Equine Electrolyte Use and Gastric Emptying (AAEP 2011)

An effective electrolyte supplement given prior to exercise serves to replace losses of ions and water via sweat and contributes to the ability of the supplemented horses to exercise for a longer duration.

Photo: Anne M. Eberhardt/The Horse

A horse’s prolonged sweating during athletic activity or travel means a need for fluid and electrolyte replacement, and horse owners commonly turn to electrolyte products for this purpose. A team of equine researchers examined one electrolyte supplement’s (ES) effect on fluid replacement and performance, and Michael Lindinger, PhD, associate professor at the University of Guelph, presented the results at the 2011 American Association of Equine Practitioners convention, held Nov. 18-22 in San Antonio, Texas,

Dehydration significantly impacts the cardiovascular system, exercise performance, and recovery, as well as affecting thermoregulation (the horse’s ability to cool its body during exercise). Dehydration also affects mental acuity. Thus, effectively replacing fluids lost through sweating is of utmost importance in maintaining peak levels of health and performance. Lindinger pointed out that horse sweat contains significant concentrations of ions, such as sodium, potassium, chloride, calcium, and magnesium and these are sustained during exercise.

Keeping this information in mind, he and colleagues tested an oral electrolyte supplement specifically designed with proportions of electrolyte content to replace ion and fluid losses in sweat ("Most supplements have seemingly random proportions of electrolytes; when this one was developed it was the first to have 'appropriate' proportions," Lindinger noted). Electrolytes marked with radioactive labels were administered through a nasogastric tube. In the first phase of the study, Lindinger examined how quickly electrolyte-supplemented resting horses cleared the supplement from the stomach (gastric emptying rate) by measuring disappearance of radioactivity from the abdominal regions using a gamma camera. Radioactivity from the electrolytes gradually diminished such that by the end of two hours, 82% of ES had emptied from the stomach.

The second phase of the study involved analyzing intestinal electrolyte absorption in horses at rest, and then exercising the horse to see if they performed better after receiving 3 litres of ES. They measured how fast sodium and potassium in the supplement appeared in blood plasma when the horses were resting. Lindinger reported that there was a more rapid uptake of potassium and sodium from the blood in ES-treated horses and that the electrolytes appeared in blood within 10 minutes of being orally administered, with sodium levels maintained during exercise and into the post-exercise period.

When investigators administered 3 liters of ES 60 minutes prior to exercise, those horses were able to exercise (at a moderate trot, about 6 mph) for 17 minutes longer than the control horses (treated with only 1 liter of plain water or 1 liter of ES), who became fatigued sooner. Providing more fluid volume to the ES-treated horses also seemed to enable better thermoregulation; these horses sweated more than the control horses. To support this, Lindinger explained that radioactive sodium given with the ES one hour before exercise appeared in sweat within the first 10 minutes of exercise and sodium levels were maintained throughout the exercise period.

He explained that dextrose in the ES enhances the small intestine’s uptake of water and sodium; while the dextrose elicits a glycemic response (glucose surges in the bloodstream), it is of a similar magnitude but shorter duration than what occurs with feeding. Most commercially available ES do not have dextrose, and this may impair test and slow absorption.

In summary, Lindinger noted, “An effective electrolyte supplement given prior to exercise serves to replace losses of ions and water and contributes to the ability of the supplemented horses to exercise for a longer duration.”

"This is the first ES supplement to be tested for effectiveness (functionality) in horses," Lindinger concluded. "It is the first study to have measured gastric emptying of an ES in horses, and to measure electrolyte absorption in horses. It demonstrates that electrolyte supplementation provides water and electrolytes from the gastrointestinal tract to the rest of the body during the exercise period, and that this is helpful for improving performance (increased exercise duration)."

About the Author

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado,
and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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